1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine having an air fuel ratio feedback control function and a feedback correction value learning function, and more particularly, it relates to a new technique that can improve air fuel ratio control performance by executing more accurate air fuel ratio learning processing in consideration of the unburnt fuel contained in the blowby gas introduced from an intake pipe in the cold state of an internal combustion engine.
2. Description of the Related Art
In the past, there have been proposed a variety of control apparatuses for an internal combustion engine having an air fuel ratio learning function to detect the generation of a blowby gas containing unburnt fuel in the cold state of the internal combustion engine, and to correct the air fuel ratio of an air fuel mixture based on the detected value of a blowby gas (see, for example, a first patent document (Japanese patent application laid-open No. H5-248288)).
In a conventional apparatus disclosed in the first patent document, a deviation between an average value and a reference value for an air fuel ratio feedback correction value after engine starting is compared with a set value, and when the deviation of the correction value indicates to be larger than the set value, a determination is made that a blowby gas has been generated, so air fuel ratio feedback control for the blowby gas is executed over a predetermined time after such a determination, and normal air fuel ratio feedback control is then executed after the lapse of the predetermined time.
Here, note that in general, the blowby gas is a gas containing an unburnt fuel and a combustion gas that are introduced into an intake pipe through a blowby gas passage after they have blown from a gap between a cylinder and a piston received therein of an internal combustion engine into a crankcase, as well as vaporized components of lubricating oil and vaporized components of fuel mixed in the oil.
As for the unburnt fuel among the components of the blowby gas, the extent or influence or impact thereof on the air fuel ratio correction varies depending upon how much the unburnt fuel is contained in the blowby gas. For example, the lower the temperature of the internal combustion engine, the lower does the volatility of fuel becomes, or the more does the sealing performance between the cylinder and the piston become, so an amount of fuel adhered to the wall surface of the cylinder increases. As a result, the amount of fuel which is contained in the exhaust gas or mixed with the lubricating oil in a combustion chamber defined in the cylinder of the internal combustion engine at the time of explosion stroke increases. Accordingly, the concentration of the fuel in the blowby gas in a warm-up process increases, too. However, since the warm-up state of the internal combustion engine varies or differs according to the environmental condition and the operating condition thereof, it is difficult to specify a blowby gas correction execution period in the conventional apparatus in terms of time.
In addition, even in case where there is no generation of blowby gas, there exist mechanical variations of the internal combustion engine itself or variations of component parts of a fuel injection system. Therefore, regardless of the magnitude of the variations, there necessarily or inevitably exist individual difference or specificity and a deviation of the air fuel ratio in the engine operating range, so it is also difficult to detect the state of generation of a blowby gas by the use of the feedback correction value of the air fuel ratio.
For example, in case where the time for execution of the air fuel ratio feedback for the blowby gas is extremely short in spite of the internal combustion engine being started in the cold state thereof in which the engine temperature is low, an air fuel ratio learning correction value is made lean by introducing the blowby gas containing a large amount of unburnt fuel into the intake pipe. Also, immediately after restarting of the engine after such an operation has been repeated, when the engine is in a low load region where the marginal range of combustion is small, there will be caused a reduction of the rotational speed, an engine stall or the like due to the leaning of the air fuel ratio.
Further, in case where the amount of injection fuel has been increased relative to normal time due to the aging or secular change, failure, etc., of component parts of the internal combustion engine, such a situation will be mis-detected as the state of generation of a blowby gas at a prescribed time at which a blowby gas correction is carried out. Accordingly, in an apparatus that performs fuel correction and air fuel ratio learning correction through normal air fuel ratio feedback as well as self-diagnosis of a fuel supply system by using these corrections, correction processing or failure detection processing can not be executed in a quick manner.
In prior art the control apparatus for an internal combustion engine, it is difficult to specify the period of execution of the correction of blowby gas in terms of time, and a deviation of the air fuel ratio in the operating range of the engine exists due to the variations of various kinds of parts even if no blowby gas has been generated. As a result, there is a problem that the generation of a blowby gas is not able to be detected by an air fuel ratio feedback correction value.
In addition, there is another problem that in case where the air fuel ratio feedback execution time for blowby gas is extremely short irrespective of cold starting, a reduction of the rotational speed, an engine stall or the like will be caused due to the leaning of the air fuel ratio immediately after restarting of the engine after the air fuel ratio learning correction value has been leaned owing to the introduction of a blowby gas.
Further, there is the following problem. That is, in case where the amount of injection fuel has been increased relative to normal time due to the aging or secular change, failure, etc., of component parts of the engine, such a situation will be mis-detected as the generation of a blowby gas at a prescribed time at which a blowby gas correction is carried out, so in the apparatus that performs self-diagnosis of the fuel supply system by using fuel correction and air fuel ratio learning correction through normal air fuel ratio feedback, correction processing or failure detection processing can not be quickly executed.